Radial flow runner for a hydraulic machine

ABSTRACT

A runner of the Francis type including a crown, a plurality of blades, each blade being defined by a pressure surface, a suction surface, an edge adjoining the high pressure side and a spaced apart edge adjoining the low pressure side. The crown includes a seal to seal the space above the crown against water from the high pressure side. The further runner includes at least one passage being capable to drain high pressure leakage water to the low pressure side. The passage includes an inlet aperture located in a portion of the crown which is exposed to high pressure leakage water. The passage is located within a blade and leads from the inlet aperture to the edge of the same blade adjoining to the low pressure side. The passage is shaped to form a continuous opening in the same edge adjoining to the low pressure side.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of PCT application No. PCT/EP2017/081659,entitled “RADIAL FLOW RUNNER FOR A HYDRAULIC MACHINE”, filed Dec. 6,2017, which is incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates generally to hydroelectric turbine or pumpinstallations with a radial flow runner of the Francis type.

2. Description of the Related Art

Hydraulic machines including a radial flow runner of the Francis typeare suffering from axial thrust applied to the runner of the hydraulicmachine. Since the sealing between the runner and the high pressure sideof the water passage cannot be made perfectly tight, water can get inthe space between the head cover of the hydraulic machine and the runnercrown resulting in a high axial thrust. To reduce the axial thrust priorart has proposed several concepts. One concept comprises balancing pipesdraining the water passing the seals to the low pressure side of thewater passage (see e.g. U.S. Pat. No. 1,820,150 to Moody). Anotherconcept comprises balance holes within the runner crown leading to therunner hub or to the space between the blades of the runner (see e.g.U.S. Pat. No. 4,086,020 to Seiichi and Syoji). Balancing pipes aregenerally expensive. The effectiveness of the prior art balancing holesdepends on the revolution speed of the runner and the blade geometry andtherefore leading not always to satisfactory results concerning thrustreduction. Especially in the case of modernization projects when anexisting runner relying on balancing holes has to be replaced by a newrunner the situation can occur that the modern blade geometry cannot beaccommodated by balancing holes of the known type and the installationof balancing pipes is impractical since the existing hydraulic machineis embedded in concrete. It is desirable in many modernization projectsto have new runners with blades which extend closer to the axis ofrotation at the trailing edge near runner crown. This geometry providesimproved performance characteristics but in many cases makes the use ofbalancing holes in the runner crown less effective at reducing thrustdue to radial pumping effects within the runner crown space below theshaft flange. In some cases where the flange connecting the runner tothe shaft is at a relatively low elevation, there may no longer besufficient space available in the runner crown flange to accommodatebalancing holes of the known type and so an alternative solution forthrust reduction is necessary.

What is needed in the art is an alternative concept for reducing theaxial thrust being less expensive than balancing pipes and easilyapplicable within modernization projects.

SUMMARY OF THE INVENTION

The present invention provides a runner of the Francis type for ahydraulic turbine or pump. The runner has a low pressure side and a highpressure side. The runner also has a crown including a seal for sealinga space above the crown against water from the high pressure side, aplurality of blades, and each blade of the plurality of blades beingdefined by a pressure surface, an oppositely facing suction surface, anedge adjoining the high pressure side of the runner, and a spaced apartedge adjoining the low pressure side of the runner. The runner furtherincludes at least one passage being capable to drain high pressureleakage water passing the seal to the low pressure side. The at leastone passage includes an inlet aperture located in a portion of the crownwhich during operation is exposed to high pressure leakage water. The atleast one passage is located within a respective blade of the pluralityof blades and leads from the inlet aperture to the edge adjoining to thelow pressure side of the same respective blade. The passage is shaped toform a continuous opening in the edge adjoining to the low pressureside.

The axial thrust can be reduced by a runner that includes at least onepassage leading from the runner crown to the trailing edge of at leastone of the runner blades. Having leakage water exiting the trailing edgemay reduce drag forces as the runner rotates and result in animprovement in hydraulic efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention,and the manner of attaining them, will become more apparent and theinvention will be better understood by reference to the followingdescription of embodiments of the invention taken in conjunction withthe accompanying drawings, wherein:

FIG. 1 is a cross-sectional view of a Francis turbine runner accordingto the present invention;

FIG. 2 is a cross-sectional view of a runner blade according to anembodiment of the present invention;

FIG. 3A shows a cross-sectional view of the runner blade of FIG. 2,taken across line 3A-3A;

FIG. 3B shows different kinds of embodiments of a cross-section view ofthe runner blade of FIG. 2, taken across line 3B-3B;

FIG. 4 is a cross-sectional view of a runner blade according to anotherembodiment of the present invention;

FIG. 5 shows a cross-sectional view of the runner blade according toFIG. 4, taken across line 5-5; and

FIG. 6 is a cross-sectional view of a runner blade according to anotherembodiment of the present invention.

Corresponding reference characters indicate corresponding partsthroughout the several views. The exemplifications set out hereinillustrate embodiments of the invention and such exemplifications arenot to be construed as limiting the scope of the invention in anymanner.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 displays schematically a cross-sectional view of a Francisturbine runner according to the present invention. The runner crown isdesignated as 11. A runner blade 2 extends between the crown 11 and theband designated as 12. The blade 2 has two edges designate by 3 and 4.The fluid entering the runner flows from edge 3 towards edge 4, whereasthe high pressure side adjoins to edge 3 and the low pressure sideadjoins to edge 4. It is clear that in pumping mode the flow directionof the fluid is reversed. The runner crown 11 includes circumferentiallocated seal 13 designated as 13. Seal 13 are construed to seal thespace above crown 11 against high pressure water. However due to theimperfection of the sealing a small amount of high pressure water willbe present in the space above the runner crown 11 leading to theundesired axial thrust. The runner crown 11 includes an inlet aperturedesignated by 6. The inlet aperture 6 is located in a portion of thecrown, which is exposed to high pressure water passing the seal 13. Theblade 2 comprises a passage designated by 5. The passage 5 leads frominlet aperture 6 to a portion of edge 4 adjoining the low pressure sidewhere the passage 5 forms an opening which is designated by 7. The axialthrust is relieved by draining the leakage water from the space abovecrown 11 directly through the passage 5 inside blade 2 to the lowpressure side. Since opening 7 is located in the edge 4 directlyadjoining the low pressure side the thrust is relieved to a high degree.In a preferred embodiment of the invention, the location of the opening7 is at an equal or larger radial distance from the axis of rotationthan the inlet aperture 6. This avoids backpressure due to the radialpumping effect of rotation. Therefore the runner according to theinvention relieves the thrust to lower values compared with the runnerof U.S. Pat. No. 4,086,020 because the balancing holes of U.S. Pat. No.4,086,020 leading to the hub and the space between the blades do notadjoin directly to the low pressure side of the runner. The radialpumping effect within the hub of U.S. Pat. No. 4,086,020 is significantand results in higher pressure above the runner and consequently higheraxial downthrust.

FIG. 2 displays schematically a cross-sectional view of a runner bladeaccording to present invention. The blade is designated as 2. The blade2 has an edge 3 adjoining the high pressure side and an edge 4 adjoiningthe low pressure side. The fluid flow is divided by the blade 2 whereasone side of the blade 2 forms the pressure surface and the other sidethe suction surface. The blade 2 shown in FIG. 2 contains a passagewhich is designated as 5. The blade 2 has an inlet apertures designatedas 6. At the edge 4, there is a continuous opening designated as 7. Thecontinuous opening 7 extends preferably over at least 15% of thedeveloped length of the edge 4 (x/L>=0.15). The extension of thecontinuous opening 7 over a relatively large area of the edge 4 ensuresthat the leakage high pressure water can pass easily to the low pressureside for a wide range of revolution numbers leading to a low axialthrust for all operation modes. Inlet aperture 6, passage 5 and thecontinuous opening 7 are forming a smooth passage through the blademinimizing losses as the leakage water flows through the blade.

FIGS. 3A-3B display schematically cross-sectional views through theblade 2 of FIG. 2 along the marked sections 3A-3A and 3B-3B. FIG. 3B-3Bdisplays three different embodiments of the continuous opening 7 whichis displayed in three different views along section 3B-3B. In the viewalong section 3A-3A it can be seen that the blade 2 comprises a basepart which is designated by 8 and a cover part which is designated by 9.The base part 8 includes either the entire suction side or pressure sidesurface of the blade as well as the entire surface of the edge adjoiningthe high pressure side and a substantial portion of the surface of theedge adjoining the low pressure side. A cavity is machined or cast intothe base part 8. The thinner cover part 9 is attached to the base part 8thus forming the gas passage 5. The cover part 9 may be metal orcomposite material, may be cast formed or machined and may be attachedby welding or by a bonding material (epoxy, glue, etc.). The topmostcross-sectional view along section 3B-3B shows a first embodiment of thecontinuous opening 7. The continuous opening 7 is confined by thepressure and suction side surfaces which meet at the trailing edge 4. Inthis first embodiment the pressure and suction side surfaces are endingrespectively at the same distance measured from the edge 3 adjoining thehigh pressure side along the section's camberline. The middlecross-sectional view along section 3B-3B shows a second embodiment ofthe continuous opening 7. In this second embodiment the pressure sidesurface extends further than the suction side surface measured from theedge 3 adjoining the high pressure side along the section's camberline.The bottom cross-sectional view along section 3B-3B shows a thirdembodiment of the continuous opening 7. In the third embodiment the edge4 adjoining the low pressure side in the region of opening 7 is profiledto minimize vortex shedding. Of course this kind of profile can bepresent over the whole length of edge 4.

FIG. 4 displays schematically a cross-sectional view of a runner bladeaccording to present invention in another embodiment. Additionally tothe blade of FIG. 2 the embodiment according FIG. 4 includes threespacer pieces one of them being designated as 10.

FIG. 5 shows a cross-sectional view along cross-section 5-5 displaying aside view of the spacer piece 10. Spacer pieces 10 are positioned withinthe passage 5 as needed to avoid the buckling of the cover part 9. Thespacer pieces 10 could be integral to the base part 8 or fixedlyattached to either the base part 8 or cover part 9. It is clear that thenumber of spacer pieces 10 is not restricted to the number of three butthere can be any number of spacer pieces 10.

The spacer pieces 10 may form an obstacle to the leakage water flow.Therefore it may be favorable that the spacer pieces are of aerodynamicshape. FIG. 6 shows the runner according to the present inventionfeaturing aerodynamically shaped spacer pieces 10.

It is clear that the embodiments shown in the figures are examples of amuch broader variety of embodiments each employing the inventive ideas.For example there could be several separate passages through one bladeleading from separate inlet apertures to several separate continuousopenings located at different portions of the edge adjoining the lowpressure side. The different passages could also be located in differentblades.

While this invention has been described with respect to at least oneembodiment, the present invention can be further modified within thespirit and scope of this disclosure. This application is thereforeintended to cover any variations, uses, or adaptations of the inventionusing its general principles. Further, this application is intended tocover such departures from the present disclosure as come within knownor customary practice in the art to which this invention pertains andwhich fall within the limits of the appended claims.

What is claimed is:
 1. A runner of the Francis type for a hydraulicturbine or pump, comprising: a low pressure side and a high pressureside; a crown comprising a seal for sealing a space above the crownagainst water from the high pressure side; a plurality of blades, andeach blade of the plurality of blades being defined by a pressuresurface, an oppositely facing suction surface, an edge adjoining thehigh pressure side of the runner, and a spaced apart edge adjoining thelow pressure side of the runner; and at least one passage being capableto drain high pressure leakage water passing the seal to the lowpressure side, and the at least one passage includes an inlet aperturelocated in a portion of the crown which during operation is exposed tohigh pressure leakage water, and the at least one passage is locatedwithin a respective blade of the plurality of blades and leads from theinlet aperture to the edge adjoining to the low pressure side of thesame respective blade, and wherein the passage is shaped to form acontinuous opening in the edge adjoining to the low pressure side. 2.The runner of claim 1, wherein the continuous opening extends over atleast 15% of the developed length of the edge adjoining to the lowpressure side.
 3. The runner of claim 1, wherein the location of thecontinuous opening is at an equal or larger radial distance from theaxis of rotation of the runner than the inlet aperture.
 4. The runner ofclaim 1, wherein in the region of the continuous opening, the pressuresurface of the respective blade extends further than the suction surfacemeasured from the edge adjoining the high pressure side along acamberline of the respective blade.
 5. The runner of claim 1, whereinthe respective blade in which the at least one passage is locatedcomprises a base part and a cover part where the base part is of asingle piece construction including the entire edge adjoining the highpressure side, the entire pressure surface of the respective blade, aswell as a portion of a surface of the edge adjoining the low pressureside, and wherein the base part contains a cavity and the cover part isattached to the base part above the cavity to form the at least onepassage.
 6. The runner of claim 1, wherein the respective blade in whichthe at least one passage is located comprises a base part and a coverpart, wherein the base part is of a single piece construction includingthe entire edge adjoining the high pressure side, the entire suctionsurface of the respective blade, as well as a portion of a surface ofthe edge adjoining the low pressure side, and wherein the base partcontains a cavity and the cover part is attached to the base part abovethe cavity to form the at least one passage.
 7. The runner of claim 6,further comprising at least one spacer piece that is located between thebase part and the cover part within the at least one passage.